In the art of manufacturing fibrous insulation, conveying mechanisms are often used to transfer material from one location in a facility to another. Typical conveying mechanisms include conveyor belts, roller lines, vibrating platforms, blowers, pneumatic conveying systems and the like.
Pneumatic conveying mechanisms include pressure systems and vacuum systems. In the art, dense phase conveying systems and dilute phase conveying systems are commonly used. Dense phase conveying systems have a low air-to-material ratio. Dense phase systems move material through a conveying line in batches, with discrete material waves or plugs separated by air pockets. Adjusting the system's valves to add less material increases the air pocket size; adding more material reduces the air pocket size.
In contrast, dilute-phase systems have a high air-to-material ratio. The material is often fluidized, or suspended in the airstream, and moves at a relatively high velocity, depending on the particle size and density. This system constantly supplies the material at the pickup point and conveys it to the system's discharge end without interruption, with no waves or plugs of material and no air pockets
Many materials may be transferred via the above systems including, but not limited to, clay, carbon black, cement sand, metals, sugar, flour, grains, pellets, chemicals, plastics, pharmaceutical materials such as tablets, and other common materials know in the art.
Another example of a process that uses conveying mechanisms for fibrous insulation material is the production of loose fill fiberglass insulation. Glass is heated in a furnace until molten and then the molten glass is supplied to a fiberizer to form veils or blankets of fiberglass. The fiberglass is then conveyed to a milling apparatus that cuts the fiberglass into smaller bodies or tufts of insulation material. The tufts then pass through a rotary valve in a duct work assembly to be collected for packaging.
The rotary valve typically includes a plurality of metal vanes rotating about a central shaft inside a housing or shell. The housing has inlet and outlet ports on either side. The vanes divide the interior of the housing into multiple isolated moveable compartments.
The rotary valve is often used to move material from areas of high pressure to areas of low pressure or visa versa without significant depressurization. Frequently, the top of the housing is open to allow insulation material to drop in via gravity. The housing is also open at the bottom to allow material to exit the valve via gravity or via an exhaust air stream. Typically, a seal arrangement is included at the end of each vane and engaging the housing inner surface. The ends of the vanes frequently have a seal material attached that slides along the inside of the housing to prevent gas from flowing around the vanes from the high pressure region to the low.
The tufts are typically conveyed through the rotary valve by a high pressure system. Further, the tufts, and gasses associated therewith, are often still significantly heated from the fiber forming process. These and other factors can create wear and tear or otherwise degrade the seals of the rotary valve that maintain the pressure difference.
The seal material is usually a reinforced elastomer. Many times in high-temperature applications, no seal material is used. Instead the metal vanes of the rotary valve are brought to close tolerance with the housing to form the seal.
At high temperatures, for example around 400 degrees Fahrenheit, a process usually requires significant sealing around a large diameter rotary valve. Especially given the large diameter, the seal has to conform to eccentricities and imperfections in the housing. In addition, material can build up around the entrance to the housing and the seal must conform to these local asperities. Materials used for the seals include plastics, such as Teflon™, and elastomers, such as silicon. These seals, however, tended to take a set, wear out, or fracture in this harsh environment.
Further, in an application where the rotary valve must present low friction against the housing, the housing can have inherent variations and eccentricities that would require the seal to have the ability to conform easily to the housing. Elastomeric seals tend to present a high friction coefficient against the housing surface. Solid seals, such as a Teflon™ seal, by DuPont, generally do not provide a tight seal to the housing.
What is needed is an improved rotary valve seal.